Monolayer Hexagonal Boron Nitride: An Efficient Electron Blocking Layer in Organic Photovoltaics

Abstract In this study, monolayer hexagonal boron nitride (h‐BN) grown via chemical vapor deposition (CVD) as an effective electron blocking layer (EBL) for the organic photovoltaics (OPVs) is proposed. Unexpectedly, it is found that h‐BN can replace the commonly used hole transport layers (HTLs), i.e., molybdenum trioxide (MoO 3 ) and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in an inverted device architecture. Here, a wet‐transfer technique is employed and a single layer of h‐BN on top of the PV2000:PC 60 BM blend is successfully placed. Analysis of the bandgap diagram shows that the monolayer h‐BN makes smaller barrier for holes but significantly larger barrier for electrons. This makes the h‐BN effective in blocking electrons while creating a possible path for the holes through tunneling to the electrode, due to the low energy barrier at the PV2000/h‐BN interface. Using h‐BN as an EBL, efficient inverted OPVs are achieved with an average solar‐to‐power conversion efficiency of 6.13%, which is comparable with that of reference devices based on MoO 3 (7.3%) and PEDOT:PSS (7.6%) as HTLs. Interestingly, the devices with h‐BN shows great light‐soak stability. The study reveals that the monolayer h‐BN grown by CVD could be an effective alternative EBL for the fabrication of efficient, lightweight, and stable OPVs.